Non-continuous orthogonal frequency division multiplexing （NC-OFDM） technology is an application of cognitive radio （CR）. In NC-OFDM communication systems， cognitive users sense the spectrum holes in authorized frequency to reduce the waste of spectrum resources. In order to ensure the communication quality of authorized users， cognitive users need to exit immediately when authorized users access， which makes the real-time requirements of NC-OFDM systems higher than those of OFDM systems. Traditional resource allocation algorithms designed for OFDM systems cannot meet real-time requirements. Considering the spectrum features of NC-OFDM systems， two fast resource allocation algorithms are proposed： Firstly， the power threshold is calculated based on the bit error rate and gain-to-noise ratio， and a single judgment is used to select the sub-channels used by the cognitive users， which reduces the dimensionality of the solution space； Secondly， the water-level is calculated directly and the power and bit allocation are initialized. Finally， based on dichotomy， the remaining resource of sorted channels （method 1） or unsorted channels （method 2） is allocated. The theoretical analyses and simulations show that the proposed algorithms have the same （method 1） resource allocation results or the similar resource allocation results （method 2） as the optimal algorithm. The calculation complexity of the proposed methods is lower， which significantly speeds up resource allocation.